The first thing you should do is rush the big and the small sub.
You can dock the small sub in the big one, and even build stuff in it. Storage and stuff. It acta amazing as a mobile base and has it's own constructor.

Counterpoint: the big sub is slow, too big and a pain in the rear end to keep powered (takes 6 power cells). I'd just focus on the little one and grab a solar upgrade when you get the moon pool. Apparently they're planning on adding stuff to recharge the big sub in the next major update so maybe it'll be more useful at that point.

Yeah but...large cells are easy to produce. You get the efficiency upgrade super easy, and with 6 full cells you can run days and days.

What is up with silver, I can find everything else pretty easily but silver continuously eludes my grasp, whether its hiding in blood grass or kelp forests, so far the best luck Ive had is finding vents where magma comes through and checking the caves in those.

The reslist place to find silver is in the kelp forest, in Sandstone Outcrops, not Limestones one. They are pretty rare.
You will find more in further away biomes. If you have a radsuit the crashsite also has more Sandstone iirc.

I think I've pretty much built what there is to build in this game... except find a sea glider fragment. Are these supposed to be so rare? Wiki says they're found in kelp forests, but I've scanned >100 kelp forest fragments now, none were sea glider ones.